Piston return and buffer system



INVENTOR. LAWRENCE J; BRUNELLE wsmwe a 1 1'2 2 w 6 4 o wM w a w H 3 f//// rA:// 7 fl 3 Z 8 6 4 7 3 wa 5 ajj r Mwz July 18, 1967 PISTON RETURN AND BUFFER SYSTEM A T TORNEV United States Patent Cfiice 3,33l,545 Patented July 18, 1967 3,331,546 PISTON RETURN AND BUFFER SYSTEM Lawrence J. Brunelie, East Haven, Conn assignor to Olin Mathieson Chemical Corporation, a corporation of Virginia Filed June 1, 1965. Ser. No. 460,056 9 Claims. (Cl. 227-) This invention relates generally to power-actuated piston tools for driving fasteners into masonry, concrete, wood, steel, or the like; and more particularly to a piston return and buffer system for suchtools.

It is an object of this invention to provide a poweractuated tool having a piston return and buffering system which will return the piston to its firing position and also absorb the energy of the piston in the event of a free-flight shot or accidental overdriving of the piston.

It is another object of this invention to provide a piston return and buffer system which is durable and can withstand repeated usage.

These and other objects may be accomplished by the provision of a piston member mounted for reciprocation within a barrel member. Means are provided which act against the piston during its power stroke to return the piston to its firing position after the fastening operation is completed. Such means absorb relatively low energy during the normal power stroke, but absorb relatively high energy in the event of additional forward movement of the piston due either to overdriving or by an accidental free-flight shot.

This invention may be more readily understood by reference to the following description of a preferred embodiment and the accompanying drawing in which:

FIGURE 1 is a longitudinal cross-sectional view of a power tool incorporating a piston return and buffer system constructed in accordance with this invention and showing the piston in its firing position;

FIGURE 2 is a transverse cross-sectional view taken along the lines 2-2 of FIGURE 1; and

FIGURE 3 is a longitudinal cross-sectional view of the tool of FIGURE 1 showing the position of the piston at the end of the normal power stroke.

Referring to the drawing, the power tool may include a hollow cylindrical barrel member 2, having a reduced breech portion 4 which forms a shoulder 6 in the internal surface of the barrel member 2. A cartridge receiving chamber 8 is provided in the end of the breech portion 4.

Threadedly attached to the forward end of the barrel member 2 is a fastener guide 10 having a longitudinal bore 12 extending therethrough. The bore 12 has a reduced portion 14 at a point adjacent the opening into the barrel member 2 which forms a shoulder 16.

A fastener 18 is shown positioned in the fastener guide 10. The fastener may include an enlarged head portion 20 and a reduced shank portion 22. The forward end of the shank portion 22 may be provided with a plastic tip or washers or other members 24 having a circular flange 26 to properly align the fastener 18 in the bore 12. As can be seen in FIGURE 1, the fastener 18 is positioned in the bore 12 with the end surface of its head portion 20 positioned against the shoulder 16.

A piston member 28 is mounted for reciprocation within the barrel member 2. The piston may include a head portion 30 having a circular flange 32 and a reduced cylindrical extension 34. Extending forwardly from the head portion 30 is a cylindrical shank portion 36.

In the firing position of the piston member 28, the flange 32 abuts the shoulder 6 in the internal surface of the barrel member 2 and the cylindrical extension 34 extends into a counterbore 38in the breech portion 4. The forward tip portion of the shank portion 36 is positioned within the reduced portion 14 of the bore 12 of the fastener guide 10.

The piston return and buffer system, indicated generally by 40, is positioned about the shank portion 36 of the piston and extends from the rearward face 42 of the fastener guide 10 to the circular flange 32 of the piston member 28.

In the preferred embodiment of the invention, the piston return and buffer system 40 comprises a plurality of stacked washer members 44. Each washer member 44 in its natural position has a shape corresponding to a hollow frustrum of a cone including an aperture 46 and a side portion 48 which is inclined With respect to a plane perpendicular to the axis of the aperture. The angle of inclination of the side portion with respect to such plane may range from about 15 to 65.

The outer ends 50 of each of the side portions 48 include a flat surface 52 which lies in a plane substantially parallel to the plane which is perpendicular to the axis of the aperture 46. Air bleed holes 54 (enlarged for the sake of clarity in the drawing) may be provided in the side portion 48.

The washers 44 are positioned within the barrel member 2 with the shank portion 36 of the piston member 28 extending through the apertures 46. As can be seen in FIGURE 1, adjacent washers are inverted with respect to each other such that groups of two washers are formed having the flat surfaces 52 on the outer ends 50 of their side portions 48 in engagement with each other. One washer of each group has a portion of its surface immediately surrounding aperture 46 in engagement with a similar portion of a washer in an adjacent group. This arrangement provides a bellows-like structure extending from the circular flange 32 of the piston member 28 to the rearward face 42 of the fastener guide 10.

Preferably, the washers 44 are constructed from a polyurethane elastomer. Such material has been found to provide the degree of durability needed in such a tool and also possesses the characteristic of being capable of absorbing a high degree of energy and returning to its original shape.

As can be seen in FIGURE 1, those washers that are closer to the fastener guide 10 when the piston member 28 is in the firing position; i.e., those in the lower half of barrel member 2, have the outermost edges of their side portions 48 in engagement with the cylindrical interior surface 56 of the barrel member 2, and the walls 58 of their apertures 46 are spaced from the shank portion 36 of the piston member 28. Those washers closer to the breech portion 4 of the barrel member 2 when the piston member 28 is in its firing position; i.e., those in the upper half of barrel member 2, have the outermost edges of their side portion 48 slightly spaced from the interior surface 56 of the barrel member 2 and the walls 58 of their cylindrical apertures 46 substanially in contact with the shank portion 36 of the piston member 28.

In operation, at the end of the normal power stroke, the piston member 28 will be positioned within the barrel member 2 as shown in FIGURE 3 with the tip of shank portion 36 of the piston member 28 spaced from the muzzle end of the fastener guide 10 by a distance equal to the exposed portion of the driven fastener. In such position, the stacked washers 44 will be collapsed and form a shut tubular column 60 of elastomeric material as shown in FIGURE 3. In the event of a free-flight shot or overdrive of the piston, this shut tubular column 60 will function as a buffer to absorb the high energy of the piston member 28.

At the end of the normal power stroke of the piston member 28, and after dissipation of the gases used to drive the piston through vent holes 62, the washers 44 will return to their original shape due to the elastic memory inherent in the elastomeric material, and thus return the piston member 28 to its firing position ready for the next fastening operation.

Since the piston member 28 is automatically returned to its firing position, a fastener'magazine 64 may be utilized with the tool of the present invention to automatically feed a new fastener into the bore 12 of the fastener guide it Any conventional magazine which includes means to urge the fasteners into the fastener guide may be used.

Due to the above-described spacing of the washers 44 with respect to the shank portion 36 of the piston and the internal surface 56 of the barrel member 2, the effects of frictional contact of the washers with the barrel and piston during movement of the piston member 28 is minimized, thus reducing the amount of heat generated which could adversely affect the composition of the washer members. It will 'be appreciated that, during the downward stroke of the piston member 28, the washers in the upper half of the barrel member have a greater relative movement with respect to the internal surface 56 of the barrel member 2 than they do with the shank portion 36 of the piston member 28. On the other hand, the washers in the bottom half of the barrel member have a greater relative movement with respect to the shank of the piston than with respect to the wall of the barrel member. Thus, it can be seen that the described arrangement utilizes the portion of the tool for centering and guiding the washers that has the least amount of relative movement with the washers.

By virtue of the particular configuration of the washers, during the normal power stroke, substantially little energy will be absorbed by the collapsing of the washers, and thus there will be little interference with the velocity of the piston which would hamper the fastening operation. However, when the washers assume their shut, tubular column position as shown in FIGURE 3, they function to absorb a high degree of energy in the event of a freeflight shot or overdrive of the piston member and prevent serious damage to the tool. After such a free-flight shot or overdrive of the piston, the washers 44 function to return the piston member 28 to its firing position.

Although reference has been made to a particular embodiment of the present invention, various modifications will readily suggest themselves to those skilled in the art and reference should be made to the appended claims to determine the scope of the invention.

What is claimed is:

1. A power-actuated tool comprising hollow barrel means, a piston mounted within said barrel means for movement between a first firing position and a second driven position, said piston having a head Portion and a reduced elongated shank portion, fastener guide means attached to said barrel means at one end thereof, said fastener guide means having a longitudinal bore communicating with the interior of said barrel means, and piston return and buifer means operably mounted between the head portion of said piston and said fastener guide, said piston return and buffer means comprising a stack of hollow, generally frusto-conical washer members of elastomeric material defining a bellowsdike structure when said piston is in its first position, said washer members being collapsible to a closed tubular column when said piston moves to said second position, said washers being disposed about the shank portion of said piston and said'stack extending from the head portion of said piston to said fastener guide, said means operable to return said piston to said first position, said means absorbing relatively little energy of the piston during movement thereof from the first position to said second position, but being capable of absorbing a relatively large amount of energy of said piston in the event of movement thereof beyond said second position.

2. In a power-actuated tool having a barrel, a piston mounted for movement between a first firing position and a second driven position, the improvement comprising piston return and buffer means operably connected between the barrel and piston, said means comprising a stack of hollow, generally frusto-conical washer members of elastomeric material defining a bellows-like structure when said piston is in its first position, said washer members being collapsible to a closed tubular column when said piston moves to said second position, said means operable to return said piston to said first position, said means absorbing relatively little energy of the piston during movement thereof from said first position to said second position, but being capable of absorbing a relatively large amount of energy of said piston in the event of movement thereof beyond said second position.

3. In the power-actuated tool of claim 2, each of said washer members comprising a polyurethane elastomer.

4. In the power-actuated tool of claim 2, each of said washer members including a central aperture and an inclined portion having an outer end, said outer end includ ing a flat surface lying in a plane substantially parallel to a plane perpendicular to the axis of said aperture, said washer members being arranged such that when said piston is in said first position, adjacent washer members are inverted with respect to each other forming groups of two washers having said fiat surfaces in engagement with each other and one washer member of each group has a portion of its side portion immediately surrounding said aperture in engagement with a similar portion of a Washer member in an adjacent group.

5. The power-actuated tool of claim 1 wherein said fastener guide includes an opening communicating with said bore and further comprising magazine means communicating with said opening for automatically posigroups of two washer members having said fiat surfaces in engagement with each other and wherein one washer member of each group has a portion of its side portion immediately surrounding said aperture in engagement with a similar portion of a washer member in an adjacent group.

7. The power-actuated tool of claim 6 wherein each of said washer members has air bleed hole means extending through its inclined side portion and said barrel means has air vent means communicating with the interior of said barrel means.

8. The power-actuated tool of claim 6 wherein when said piston is in its firing position, those washer members closest to said head portion are spaced from the internal surface of said barrel member and have the wall portion of their apertures in contact with said shank portion, and said washer members closest to said fastener guide are in contact with the internal surface of said barrel member and have the wall portion of their apertures spaced from the shank portion of said piston.

9. A power-actuated tool comprising hollow barrel means, a piston mounted Within said barrel means for movement between a first firing position and a second driven position, said piston having a head portion and a reduced elongated shank portion, fastener guide means attached to said barrel means at one end thereof, said fastener guide means having a longitudinal bore communicating with the interior of said barrel means, a plurality of stacked, hollow, frusto-conical elastomeric washer members positioned about said shank portion and' extending from said fastener guide means to said head portion, each of said washer members including a central aperture and an inclined side portion having an outer end,

said outer end including a fiat surface lying in a plane substantially parallel to a plane perpendicular to the axis of said aperture, said washer members being arranged in the firing position of the tool such that adjacent Washer members are inverted with respect to each other forming groups of two washer members having said flat surfaces in engagement with each other and wherein one Washer of each group has a portion of its inclined side portion immediately surrounding said aperture in engagement with a similar portion of a washer member in an adjacent group, said washer members further being collapsible upon movement of the piston from its first to its second position, whereupon when said piston is in its second position, said washer members form a closed, solid, tubular column, air vent means Within said barrel means cornmunicating with the interior thereof, air bleed hole means in the side portions of each of said washer members, and magazine means operably connected to said fastener guide means and communicating with the bore thereof for automatically positioning a fastener in said bore.

References Cited UNITED STATES PATENTS 65,790 6/ 1867 Belleville. 2,723,532 11/1955 Smith. 2,724,116 11/ 1955 Termet 2279 2,729,618 1/1956 Muller et al 267-1 10 2,902,273 9/ 1959 Hoenner 2671 3,126,630 3/1964 Catlin et al. 2271O XR 3,172,119 3/1965 Siddons 227'10 XR FOREIGN PATENTS 15 744,822 2/ 1956 Great Britain.

GRANVILLE Y. CUSTER, JR., Primary Examiner. 

1. A POWER-ACTUATED TOOL COMPRISING HOLLOW BARREL MEANS, A PISTON MOUNTED WITHIN SAID BARREL MEANS FOR MOVEMENT BETWEEN A FIRST FIRING POSITION AND A SECOND DRIVEN POSITION, SAID PISTON HAVING A HEAD PORTION AND A REDUCED ELONGATED SHANK PORTION, FASTENER GUIDE MEANS ATTACHED TO SAID BARREL MEANS AT ONE END THEREOF, SAID FASTENER GUIDE MEANS HAVING A LONGITUDINAL BORE COMMUNICATING WITH THE INTERIOR OF SAID BARREL MEANS, AND PISTON RETURN AND BUFFER MEANS OPERABLY MOUNTED BETWEEN THE HEAD PORTION OF SAID PISTON AND SAID FASTENER GUIDE, SAID PISTON RETURN AND BUFFER MEANS COMPRISING A STACK OF HOLLOW, GENERALLY FRUSTO-CONICAL WASHER MEMBERS OF ELASTOMERIC MATERIAL DEFINING A BELLOWS-LIKE STRUCTURE WHEN SAID PISTON IS IN ITS FIRST POSITION, SAID WASHER MEMBERS BEING COLLAPSIBLE TO A CLOSED TUBULAR COLUMN WHEN SAID PISTON MOVES TO SAID SECOND POSITION, SAID WASHES BEING DISPOSED ABOUT THE SHANK PORTION OF SAID PISTON AND SAID STACK EXTENDING FROM THE HEAD PORTION OF SAID PISTON TO SAID FASTENER GUIDE, SAID MEANS OPERABLE TO RETURN SAID PISTON TO AND SAID FIRST PISTON, SAID MEANS ABSORBING RELATIVELY LITTLE ENERGY OF THE PISTON DURING MOVEMENT THEREOF FROM THE FIRST POSITION TO SAID SECOND POSITION, BUT BEING CAPABLE OF ABSORBING A RELATIVELY LARGE AMOUNT OF ENERGY OF SAID PISTON IN THE EVENT OF MOVEMENT THEREOF BEYOND SAID SECOND POSITION. 